There is a electrical code for outdoor service equipment. Which is any electrical meter and panel coming off that meter. NEC 110.26(A)& 110.26(F). The open zone around service equipment must have 6.6 feet head room, 3 foot in depth and 30 inches or width of equipment from side to side. So all you need to be safe is 30 inches.
This applies to access to the equipment, not to the mounting of equipment on the wall adjacent to the equipment.
This basicly says that the area in front of service equipment must be at least 30" wide (or width of equipment if more than 30" wide), 36" from FRONT of equipment to nearest obstruction, and 6.5' high.
110.26(f) defines the dedicated equipment space, basicly saying that you can't mount non-electrical items above panels below the 6' level or structural ceiling, whichever is less, with the exception allowing for false ceilings within that space. This extends the virtual width and depth of the equipment up to the 6' level.
